Answer:
The terms are already in lowest form. The factors of 21 are 21 and 1, and 3 and 7. The factors of 18 are 1 and 18, 2 and 9, and 3 and 6. The factors of 28 are 1 and 28, 2 and 14, and 7 and 4. None of them match up so it is as low as it can be.
Step-by-step explanation:
the greatest common factor is x. because
21, -18, and 28 do not have any shared factors
